Internal combustion engines require oil, or some other form of lubricant, to lubricate the various moving parts of the engine. In standard internal combustion engines, this is accomplished by storing the oil in a crankcase and supplying oil from the crankcase to the various moving parts through some type of distribution system. The oil from the various parts of the engine is then returned to the crankcase via some type of drainback system, such as a drainback passage.
For example, oil from the crankcase of a standard internal combustion engine is supplied from the crankcase to the valve train to lubricate the valves, rocker arms, and other parts of the valve train. The oil from the valve train passes through the cylinder head of the engine and back to the crankcase through a drainback passage.
However, under certain operating conditions, this standard drainback system poses some drawbacks. For example, under conditions when high crankcase pressure exists, oil from the crankcase can be forced backwards through the drainback passage, possibly filling the cylinder head and valve box with oil. Similarly, if the engine were operated at an elevated angle (e.g. tilted backwards), oil from the crankcase could flow backwards through the drainback passage, again possibly filling the cylinder head and valve box with oil. If the cylinder head and valve box were filled with oil, the operation of the air intake, air exhaust, and spark plug, which are located in the cylinder head, could be interrupted and oil could possible flow through the valves into the cylinder.
It would therefore be advantageous if an internal combustion engine could be designed that prevented oil from the crankcase from filling the cylinder head and/or valve box of the engine. In particular, it would be advantageous if the oil drainback system of the internal combustion engine could be designed to allow the flow of oil through the drainback passage from the valve box to the crankcase during normal operation and to prevent the flow of oil through the drainback passage from the crankcase to the valve box during certain operating conditions, such as when high pressure is present in the crankcase or during operation at an elevated angle.